Stuðlabergsfoss waterfall - East Iceland
Iceland has rather more of it's share of large waterfalls - best seen in LARGE.
This is a fall below the 118m Hengifoss which is the largest waterfall in East Iceland and the third (or maybe fourth) tallest in Iceland overall. Called Stuðlabergsfoss, I find this more impressive than the fall above because of the interesting arrangement of basalt columns formed in the particularly thick lava flow flanking the waterfall.
The hexagonal columns are formed as the molten lava cools quickly and can be exaggerated when the lava flows over saturated ground and the resulting steam forces it's way through the flow, cooling it as it goes. In this case the columns appear to have curved over towards the waterfall. Of course, it must have happened round the other way - the waterfall exploiting a weakness in the rock where the cooling cracks had been at their greatest, but it is hard to see it that way. Also, beneath the columns there are some lava tubes (one just visible on the right), where lava has flowed in a tube, cooling on the outside and then running out, so the tube empties to leave an open tube.